The present invention relates to inflation devices for inflation of buoyancy bodies such as lifejackets or liferafts.
A well known type of life-jacket comprises an impermeable outer skin defining an internal cavity. Typically, a proportion of this internal cavity is filled with a buoyant material to provide an initial, low, level of buoyancy and the skin is inflated by injection of gas to provide a higher level of buoyancy when needed. Alternatively, in some lifejackets the internal cavity is initially empty, and must be inflated to provide any buoyancy.
It is known to provide lifejackets with an externally mounted cylinder containing pressurised gas for inflation of the outer skin. The cylinder is connected via a one way valve (typically a Schraeder valve) to a passage in flow connection with the internal cavity.
The neck of the externally mounted cylinder is initially sealed by a metal closure diaphragm, and a mechanism is provided whereby the diaphragm is punctured when, for example, an actuating tag is pulled, causing inflation of the lifejacket.
Such lifejackets suffer from a number of disadvantages. The external cylinder is inconvenient to the wearer as it tends to catch on obstacles (which is a particular drawback on boats, which provide a large number of obstacles such as ropes, ladders etc). It is also vulnerable to physical damage by impacts, and is unprotected from the corrosive effects of water. Known cylinders typically have a cadmium outer plating which, in combination with the metal components of the valve and the actuating mechanism and in the presence of salt water, gives rise to electrolytic corrosion.
Another problem associated with these known lifejackets arises at low temperatures. The cylinders are filled with CO.sub.2 gas which, as it expands, can freeze, thereby blocking the (usually restricted) passage through which the gas enters the internal cavity.
There have been attempts in the past to overcome these problems by mounting the gas cylinder within the internal cavity of the lifejacket. In one such lifejacket an inflation assembly comprising the cylinder and the mechanism for puncturing its metal closure diaphragm is placed loose within the internal cavity, being accessible only via a sealable hole in the outer skin.
To pierce the closure diaphragm, the user locates the inflation assembly by feel through the outer skin, and then squeezes a handle through the skin to cause inflation.
This operation requires time and a degree of manual dexterity, which can be problematic since in emergencies it is often very important to inflate a lifejacket quickly.
Further, exposure to cold, particularly cold water, can make any kind of manipulation very difficult the user's hands may become too numb to be used effectively, so that inflation of the lifejacket is hard to achieve.
A further type of lifejacket with an internally mounted inflation cylinder is described in GB 2171962. In this case, the outer skin is formed with a projecting elongate pocket. A movable lever of the inflation assembly projects into the said pocket, and a cord is tied to the distal end of the outside of the pocket surrounding both the pocket and the lever so that pulling on the cord moves the lever, puncturing the metal closure diaphragm and inflating the lifejacket.
This lifejacket is complicated to manufacture, since the outer skin must be formed to provide the projecting pocket. It is also complicated to assemble; the inflation assembly must first be inserted through a gap in a seam of the outer skin. Then the movable lever must be located in the pocket, and the cord tied around the pocket, retaining the lever, and the gap in the seam must then be welded closed.
The lifejacket in question is not reusable. The inflation assembly is permanently sealed within the jacket, so that after one inflation (which exhausts the gas cylinder) the cylinder cannot be replaced.
Additional problems arise where the inflation device in question is adapted to be automatically triggered when its associated buoyancy body is placed in water. Such automatic inflation devices are used on lifejackets and liferafts, and several types are known.
Some known automatic inflation devices are electrically controlled, being responsive either to the reduction in resistance between two external electrical contacts when both are immersed in water, or to the electromotive force generated by a sea water actuated electric cell. In the latter type of device salt water acts as the electrolyte of the cell.
When used to cause inflation of buoyancy bodies, electrical release devices suffer from serious disadvantages. Devices which rely on a reduction in resistance must include a battery or cell, which is certain to discharge over time and so require periodic maintenance. Large numbers of life vests are stored in ships and aeroplanes, and must be kept in constant readiness, so that it is important to maximize the service interval of the release device.
Further, electrical release devices must cause inflation of a buoyancy body by electrical or electromechanical means, and known ways of achieving this are not ideal. One type of device uses a retainer which is electrically melted to release an inflation mechanism, but low water temperatures can prevent melting of the retainer and so cause the unit to fail with potentially life threatening consequences. Another type of device uses an electronically ignited explosive charge to release gas, but there are concerns regarding the safety of detonating such a charge on a personal flotation device.
Still another important disadvantage of electrically actuated release devices in the present context is that they can be accidentally released, e.g., by humidity or spray.
It is also known to provide a mechanical release device to cause automatic inflation of a buoyancy body. One such device is described in GB 2051212 and comprises first and second internal chambers (the first chamber being open to ingress of water, while the second chamber is sealed) separated from each other by a spring biased diaphragm which is movable by hydrostatic water pressure within the first chamber. Motion of the diaphragm directly actuates a spring loaded gas release device.
One of the problems associated with such known mechanical release devices actuated by hydrostatic pressure arises from the fact that the depth to which a buoyancy body is immersed is typically small. The small resultant hydrostatic pressure frequently does not produce a large enough force to overcome friction in the release device. The problem is compounded in mechanical devices of the above described type by the fact that the diaphragm must be moved against the force caused by air within the second (sealed) internal chamber. Since the air within the second chamber cannot escape, it effectively biases the diaphragm against motion in the release direction.
For these reasons, reliable inflation is often not achieved using known devices responsive to and actuated by hydrostatic pressure. Again, this can cause non-inflation of a life vest or liferaft which can endanger life.
Another type of automatic release device suited to use in conjunction with inflatable buoyancy bodies comprises a retainer which is softened or dissolved upon contact with water. For example, a salt plug may be used to retain a spring loaded gas release mechanism, so that when the salt plug is exposed to water and dissolved, the gas release mechanism is released.
The major problem with this known type of release mechanism is that the retainer tends to absorb moisture from the air, and over time this leads to unintentional softening of the retainer, with consequent release of gas and inflation of the buoyancy body. For this reason, the retainer in buoyancy bodies with this type of release must be periodically replaced.